How to write an ipv6 udp echo client?

[yinkaisheng]

I use Windows 10, python 3.12.6 and anyio 4.6.
I wrote the code:

import sys
import socket
import anyio

async def server():
    print('server starts')
    async with await anyio.create_udp_socket(family=socket.AF_INET6, local_host='::', local_port=25000) as udp:
        async for packet, (host, port) in udp:
            print(f'recv from {host} {port}: {packet}')
            print(f'send to {host} {port}: {packet}')
            await udp.sendto(packet, host, port)

async def client():
    host, port = '::1', 25000
    async with await anyio.create_udp_socket(family=socket.AF_INET6) as udp:
        laddr = udp.extra(anyio.abc.SocketAttribute.local_address)
        print(f'client {laddr}')
        for i in range(4):
            data = f'hello {i}'.encode()
            print(f'send to {host} {port}: {data}')
            await udp.sendto(data, host, port)
            resp, raddr = await udp.receive()
            print(f'recv from {raddr}: {resp}')

if __name__ == '__main__':
    func = server if sys.argv[1] == 'server' else client
    anyio.run(func)

When a client runs, the server doesn't receive the data.

[smurfix]

Meh. Works on Linux, unsurprisingly.

What happens if you use IPv4?

[agronholm]

It also works fine on the trio backend, even against localhost.

[agronholm]

It's worth noting that we're skipping asyncio ipv6 UDP tests "due to a known bug" (python/cpython#83329). At least there used to be a problem with IOCP support around this, but I don't know if this is still the case. At least the upstream issue has been closed.

[agronholm]

Relevant: https://github.com/agronholm/anyio/blob/master/tests/test_sockets.py#L115

[agronholm]

If I comment out the use of that fixture, the IPv6 UDP tests hang.

[yinkaisheng]

OK.